TruD is a member of a family of pseudouridine synthases that is widely conserved, yet unrelated to the families of pseudouridine synthases characterized previously [Kaya03]. The crystal structure showed that the protein consists of two domains, a catalytic domain with a fold similar to other pseudouridine synthases, and an insertion domain with a novel fold [Kaya04, Ericsson04, Ericsson04a, Hoang04a].